A) Field of the Invention
The present invention relates to a solid state image pickup device and more particularly to a solid state image pickup device having a number of pixels each having two photosensitive fields.
B) Description of the Related Art
A CCD solid state image pickup device and a MOS solid state image pickup device are known, the former transferring signal charges by using charge coupled devices (CCDs) and the latter amplifying and outputting an image signal from a photosensitive element. As photosensitive elements, photodiodes are mainly used and a number of photodiodes (pixels) are disposed in a light receiving area in a matrix shape. As the layout of photosensitive elements, a square matrix layout and a honeycomb layout are known. The former disposes photosensitive elements along row and column directions at constant pitches and the latter disposes photosensitive elements along row and column directions by shifting the positions of every second pixels (e.g., by shifting the positions by a half pitch).
For a solid state image pickup device having on-chip color filters, a color filter layer is formed on a semiconductor chip with photosensitive elements and signal transfer units. In many cases, on-chip micro lenses are disposed on the color filter layer to efficiently guide incident light to photosensitive elements.
In order to obtain image signals having a high resolution, it is desired to increase the number of pixels. Although all the pixels have generally the same shape, image signals obtained from respective pixels do not have the same function and importance. For example, in order to obtain a luminance signal which governs the resolution, it is necessary to use a signal having the amount of light containing light in the whole visible range or in a green range. If a luminance signal is obtained from a green signal, a large number of green pixels are desired in order to obtain an image signal having a high resolution.